When considering the role of neuroscience in modern society, the issue of a brain-machine interface (e.g., between a human brain and a computer) is one of the central problems to be addressed. Indeed, the ability to design and build new information analysis and storage systems that are light enough to be easily carried, has advanced exponentially in the last few years. Ultimately, the brain-machine interface will likely become the major stumbling block to robust and rapid communication with such systems.
To date, developments towards a brain-machine interface have not been as impressive as the progress in miniaturization or computational power expansion. Indeed, the limiting factor with most modern devices relates to the human interface. For instance, buttons must be large enough to manipulate and displays large enough to allow symbol recognition. Clearly, establishing a more direct relationship between the brain and such devices is desirable and will likely become increasingly important.
With conventional means, brain activity can be recorded from the surface of the skull. In the case of electro-encephalography (EEG), electrodes are placed on the skull and record activity occurring on the surface of the brain. In the case of magneto-encephalography (MEG), recording probes are also placed on the surface, but through triangulation brain activity can be mapped in three dimensions.
Such methods as EEG and MEG, while minimally invasive, suffer from poor resolution and distortion due to the deformation of electromagnetic fields caused by the scalp and skull. To overcome these limitations with known technology requires the much more invasive option of opening the skull and inserting electrodes into the brain mass. Similarly, to stimulate the brain as is done therapeutically for some patients with Parkinson's disease or the like, the skull must be opened and electrodes inserted.
As the need for a more direct relationship between the brain and machines becomes increasingly important, a revolution is taking place in the field of nanotechnology (ntechnology). Nanotechnology deals with manufactured objects with characteristic dimensions of less than one micrometer. It is the inventors belief that the brain-machine bottleneck will ultimately be resolved through the application of nanotechnology. The use of nanoscale electrode probes coupled with nanoscale electronics seems promising in this regard.
To date, the finest electrodes have been pulled from glass. These microelectrodes have tips less than a micron in diameter and are filled with a conductive solution. They are typically used for intracellular recordings from nerve and muscle cells. A limitation is that activity is recorded from only one cell at a time. It has been possible, however, to obtain recordings from over 100 individual cells using multi-electrode arrays. Nonetheless, this is an invasive procedure as the electrodes are lowered into the brain from the surface of the skull.
In addition to probing large numbers of points in the brain, the need also exists for processing the large number of signals thus captured and analyzing them in a meaningful way. Methods for processing and displaying signals from multiple sites within the brain have been developed for multi-electrode work with animals and for MEG work with human subjects.
A robust and non-invasive way to tap, address and analyze brain activity that is optimized for future brain-machine interaction is disclosed, for example, in U.S. Published Application No. U.S. 2004/0133118, which is incorporated herein by reference. Nevertheless, a need exists for the use of nanowires with greater biocompatibility and biodegradation thus allowing for greater brain interface. In particular, contact between blood and a biomaterial results in a rapid activation of the coagulation and complement systems. While thrombin and other activated clotting factors may be diluted under high blood flow conditions, insertion of a nanowire may alter blood flow and or cause turbulence that could promote adhesion of platelets. Although many polymers are biocompatible, not all are degradable. Degradation or dissolution changes the shape, size or mass of a polymer. While hydrolysis is the most common mode by which polymers degrade, oxidation and enzymatic, cellular or microbial degradation can also occur. Greater biocompatibility of the nanowire will result in less disruption of blood flow and will enhance the ability to tap, address and analyze the brain.
Similarly, current metallic electrodes are easily distorted or even fractured with the application of minimal force. As such, there is a need for more resistant nanowires with greater flexibility and resistance to fatigue which will withstand impact with particulates in the blood.
In addition to serving as a means of interacting with machines, a brainmachine interface could also be useful in the diagnosis and treatment of many neurological and psychiatric conditions.
Furthermore, current metallic electrodes conduct both longitudinally, as well as laterally along the axis of the wire. As such there is a need for a nanowire which can conduct longitudinally only to better direct the location of charge for the treatment and testing of many neurological and psychiatric conditions. Similarly, current electrodes lack the ability to selectively deflect along any axis and thus are limited in the specificity to which they can be directed.
The ability of polymers to act as electrical insulators is the basis for their widespread use in the electrical and electronic fields. However, material designers have sought to combine the fabrication versatility of polymers with many of the electrical properties of metals. There are instances when an increased conductivity or relative permittivity of the polymer is warranted, such as in applications which require antistatic materials, low-temperature heaters, electromagnetic radiation shielding and electric field grading. A few select polymers, such as polyacetylene, polyaniline, polypyrrole and others, can be induced to exhibit intrinsic electronic conductivity through doping, though these systems often tend to be cost prohibitive and difficult to fabricate into articles.